1. Field of the Invention
The present invention relates in general to a wheel cover detachably attached to a wheel rim for enclosing and decorating the same, and more particularly to a plastic wheel cover which is equipped with a spring-biased fastening device through which the cover is detachably connected to the wheel rim.
2. Description of the Prior Art
Hitherto, plastic wheel covers have been widely used because of the light weight, high durable, rustproof and easily moldable characteristics of the plastics from which the cover is produced. However, the plastic wheel covers have some drawbacks which originate from a notable permanent set exhibited by the plastics after long use thereof. This notable permanent set has disabled the plastic wheel cover from having, by themselves, resilient catching pawls which are used for retaining the cover to the wheel (viz., the wheel rim). Thus, usually, a plurality of metal springs or the like are employed for assisting or assuring a prolonged retaining function of the catching pawls. However, mounting numerous metal springs on the plastic wheel cover has brought about a complicated configulation of the fastening device on the cover. Thus, hitherto, manufacturing or molding of the plastic wheel covers of such type with high productivity has been difficult.
In view of these drawbacks, various measures have been hitherto proposed, some being disclosed in Japanese Patent First Provisional Publications Nos. 62-160902, 62-258802 and 62-279101, which disclose a fastening device integrally provided on the plastic wheel cover. That is, the fastening device disclosed by them comprises a plurality of catching pawls integral with a plastic cover proper and circularly arranged on the cover, a plurality of spring holders integral with the cover and circularly arranged on the cover and a ring spring held by the holders in a manner to bias the catching pawls radially outwardly. The applicants have noted that some of the drawbacks as mentioned hereinabove are solved by the fastening device of the measure disclosed by the references. However, due to its inherency in construction, the fastening device is obliged to have bulky catching pawls and thus the degree of freedom in design of the cover is considerably limited. Beside, the resilient deformation of the ring spring is considerably restricted thereby limiting the biasing force produced by the ring spring. As is known, if the biasing force of the ring spring fails to be set at a desired level, fitting the cover to the wheel (viz., wheel rim) is not carried out with a comfortable fitting feeling. Furthermore, in a severe case, the wheel cover is disconnected from the wheel during running of the motor vehicle.